distinguishes low vitality from inorganic processes. Hence, our formula as further amended reads thus:--Life is a definite combination of heterogenous changes, both simultaneous and successive. Finally, we shall still better express the facts if, instead of saying _a_ definite combination of heterogeneous changes, we say _the_ definite combination of heterogeneous changes. As it at present stands, the definition is defective both in allowing that there may be _other_ definite combinations of heterogeneous changes, and in directing attention to the heterogeneous changes rather than to the definiteness of their combination. Just as it is not so much its chemical elements which constitute an organism, as it is the arrangement of them into special tissues and organs; so it is not so much its heterogeneous changes which constitute Life, as it is the co-ordination of them. Observe what it is that ceases when life ceases. In a dead body there are going on heterogeneous changes, both simultaneous and successive. What then has disappeared? The definite combination has disappeared. Mark, too, that however heterogeneous the simultaneous and successive changes exhibited by such an inorganic object as a volcano, we much less tend to think of it as living than we do a watch or a steam-engine, which, though displaying changes that, serially contemplated, are largely homogeneous, displays them definitely combined. So dominant an element is this in our idea of Life, that even when an object is motionless, yet, if its parts be definitely combined, we conclude either that it has had life, or has been made by something having life. Thus, then, we conclude that Life is--_the_ definite combination of heterogeneous changes, both simultaneous and successive.